Cataract often develops in aging eyes. The standard of care is to perform a cataract surgery by extracting the opaque natural lens, and replacing it by implanting an artificial intraocular lens into the capsular bag, thereby restoring healthy vision. However, after the surgery has been completed, intraocular lenses (IOLs) sometimes shift, or move away from the position they were surgically implanted in the capsular bag of the eye. This movement can shift the IOL focal point away from its intended location, typically on the retina, thereby leading to a deterioration of the optical performance of the IOL. Further, uncertainties in the eye's healing process, errors in measurements of the eye prior to surgery, and physician errors in the choice and the placement of the IOL can also contribute to a non-optimal surgical outcome. This deterioration or reduction of the optical performance often makes the difference between the patient needing to wear eye glasses after the surgery or not, and thus is a key factor of the post-surgical patient satisfaction.
Light adjustable intraocular lenses (LALs) offer a solution for this problem. If a patient returns to the doctor after the surgery to report dissatisfaction with the optical outcome because the LAL was misplaced, shifted, or was not the best selection, the doctor can mitigate the patient dissatisfaction by adjusting the LAL optical performance non-invasively. In detail, the doctor can perform a diagnostic process to determine the cause, nature and degree of the optical underperformance of the LAL. Then, the doctor can calculate what change of the optical characteristics of the LALs can compensate the underperformance. Finally, the doctor can perform an illumination procedure on the LAL to bring about the calculated change.
This adjustment is made possible by fabricating the LALs from photopolymerizable macromers, interspersed with a photoinitiator. When the doctor irradiates the LAL with a spatially modulated light source, typically emitting an UV light, the UV absorbing photo-initiator induces the photopolymerization of the macromers. The selected radial intensity profile of the irradiating UV light induces the polymerization with a corresponding radial profile. Photopolymerizing with a radial profile changes the shape of the LAL, and therefore changes the optical characteristics of the LAL. Thus, irradiating the LAL with an intensity profile changes the LAL to achieve the optical characteristics the doctor calculated to compensate the LAL's post-implantation underperformance. LAL systems and devices have been described extensively in the commonly owned U.S. Pat. No. 6,450,642, “Lenses capable of post-fabrication power modification” by J. Jethmalani et al., which is hereby incorporated in its entirety by reference.
FIGS. 1A-D illustrate aspects of this light adjustment procedure. FIG. 1A illustrates that when the LAL axis is aligned with the optical axis of the LAL irradiation system, then the beam intensity profile of the UV light beam is centered and aligned with the LAL. FIG. 1B illustrates that in the case of such alignment, the shape change induced in the LAL by the UV beam is aligned and centered with the LAL axis.
FIG. 1C illustrates the case when the LAL is not aligned with the LAL irradiation system, and thus the LAL axis is not aligned with the irradiation system axis. In this case the irradiating beam intensity profile of the UV light beam is not centered relative to the LAL axis. FIG. 1D illustrates that the shape change induced by the UV light beam in this misaligned LAL will be misaligned with the LAL axis. The optical characteristics and performance of the LAL with such a misaligned shape-change can be quite different from what the doctor calculated and planned. LALs with misaligned shape change typically do not achieve the compensation the doctor planned, and thus do not mitigate the patient's dissatisfaction. For this reason, aligning the LAL axis with the LAL irradiation system axis is important for the success of the lens adjustment procedure, and is a high priority for the design of the LAL irradiation system.
In today's LAL irradiation procedures, the eye, and the LAL in it, are aligned with the LAL irradiation system by the surgeon immobilizing the LAL manually. While this is an efficient approach, the alignment can be imperfect, and the slight shaking of the surgeon's hand may blur the irradiation pattern formed in the LAL. For all the above described reasons, any improvement towards better and more stable alignment between the LAL irradiation system and the LAL itself will lead to further improvements in the visual outcomes of cataract surgeries, and in patient satisfaction.